Storage media for computers and other types of electronic devices generally come in two types: volatile memory and non-volatile memory. Volatile memory loses its contents when power is no longer being supplied to the memory, whereas non-volatile memory maintains its contents even when power is not being supplied to the memory. The most common type of volatile memory is random-access memory (RAM), which is most commonly available as and implemented as an integrated circuit (IC). The term data storage medium is used herein in a broad sense, and encompasses IC memory, as well as other types of data storage media.
By comparison, non-volatile memory has perhaps more commonly been available as and implemented as magnetic and optical media, including hard disk drives, floppy disks, compact disc read-only memories (CD-ROM""s), CD re-writable (CD-RW) discs, and digital versatile discs (DVD""s), among others. Historically, non-volatile memory implemented as an IC was primarily available as ROM that were not re-recordable, such as hard-wired ROM and programmable ROM (PROM). More recently, IC non-volatile memory has become available as various types of flash memory, which is more technically known as electrically erasable PROM (EEPROM).
IC-based data storage media is typically read from and, where applicable, written to, by directly using electric signals. By comparison, magnetic and optical data storage media is typically read from, and where applicable, written, to using magnetic sensors and optical sensors, where the latter usually include some type of illuminating beam. However, U.S. Pat. No. 5,557,596 describes a data storage medium that can be implemented as an IC, but that is read from and written to using an illuminating beam. A phase-changeable layer is present that can be switched between two different phases by being subjected to the illuminating beam. The two phases correspond to different logical values, such as binary one and binary zero.
For reading the logical value stored in the phase-changeable layer, the medium is subjected to the illuminating beam at a low intensity. This induces current within the medium, which is then detected and correlated with the current phase of the re-recordable storage medium to determine the logical value stored in the medium. However, the current is relatively small, making it difficult to detect without error. Any present noise risks masking the current, as well as any material imperfections in the medium, which can cause erroneous logical values being read, affecting the accuracy of the medium as a data storage device.
For this and other reasons, therefore, there is a need for the present invention.
A re-recordable data storage medium of one embodiment includes a substrate layer, a phase-changeable layer, and an intermediate layer. The substrate layer has a semiconductor type selected from p-type and n-type. The phase-changeable layer has a first phase corresponding to a first storable logical value, and a second phase corresponding to a second storable logical value. The phase-changeable layer has a semiconductor type identical to that of the substrate layer. The intermediate layer is between the phase-changeable layer and the substrate layer, and has a semiconductor type opposite to that of the phase-changeable and substrate layer. The substrate, phase-changeable, and intermediate layers act as a transistor under selective illumination of the phase-changeable layer.